Soil seed bank resilience after rangeland conversion: implications for restoring abandoned agricultural lands.

Abstract

Soil seed banks (SSBs) are crucial for ecosystem recovery, but their resilience to land-use change in semi-arid systems remains poorly understood. In the Middle East, most rangelands have been subjected to intensive grazing for years (grazed rangeland, GR), while others have either been excluded from grazing (ungrazed rangeland, UR) or either converted into various agricultural land-use types, including wheat cropland (WL), legume cropland (LL), horticultural land or orchard (HL), and abandoned land (AL). We compared SSB composition and density across plant functional groups (annuals, perennials, forbs, and grasses) at 0-5 cm and 5-10 cm soil depths under varying land-use and grazing intensities. Results showed that cultivated lands had lower SSB densities for all functional groups compared to intact ungrazed rangelands. These differences were most pronounced in the upper soil layer, where the highest total SSB densities were recorded in UR and LL and lowest in WL and HL. Annual SSB densities were highest in UR and LL, lowest in WL. Perennial densities were low overall, being highest in UR and lowest in HL and GR. Overall, our findings suggest that the conversion of natural rangelands into agricultural lands leads to SSB depletion. Furthermore, intensive grazing in rangelands appears to exert a more pronounced negative impact on SSB than conversion to agricultural use. Abandoned lands, even several years after abandonment, showed critically depleted SSBs, revealing that passive recovery is unlikely and that SSB depletion severely hinders ecological restoration, emphasizing the need to integrate SSB assessments into restoration planning for land-use changes.